Vocal learning relies upon the ability to make comparisons among the motor patterns used to drive the musculature controlling phonation and respiration, the auditory consequences of those motor patterns, and the auditory model which is to be matched. These comparisons in turn are dependent upon the existence of interactions between the auditory and motor representations of vocalizations in the brain. The regulation of auditory inputs to the vocal motor centers during song learning, song production, and song processing is the focus of this proposal. Preliminary results on a neural mechanism which inhibits auditory inputs to the song motor system, and which varies in its effect during development, are reported. Neuroanatomical, electrophysiological, lesion, and behavioral studies are outlined. These studies are designed to define the sites of action and neural components of the circuits mediating the inhibition of auditory responses in the telencephalic song system, as well as the development of the circuit as related to the stages of song learning. Auditory inhibition in the song systems of open-ended and closed-ended learners will also be investigated, and the auditory feedback requirements for vocal plasticity of the temporal organization of song in closed ended- learners that have completed song development (as reported in the Preliminary Studies) will be investigated and compared to song development. The perceptual consequences of auditory - motor interactions and the irregulation by inhibition circuits would be investigated using tightly controlled playback studies, and natural song stimuli altered by surgical or neural manipulations to singing birds. Knowledge of the means by which auditory inputs affect motor activity - and learned motor patterns affect auditory processing - would help in understanding the neural processes underlying developmental and adult plasticity and would also have implications for the study of the methods brains use to associate and integrate information from different modalities.